Metals in the sporulation phosphorelay: manganese binding by the response regulator Spo0F

As a part of studies on the structural characterization of the components of the sporulation phosphorelay in Bacillus subtilis, the crystal structure of the manganese derivative of an intermediate signal transducer, Spo0F, has been elucidated at 2.25 Å resolution. The calcium complex and the apo structures have been analyzed previously. In apo Spo0F, the active-site cation cavity is only partially formed and it only becomes completed upon metal coordination. The carbonyl of Lys56 is coordinated to the metal and interestingly the side chain of Lys56 exists in a variety of conformations in the three crystal structures of Spo0F. The affinity of the magnesium ion for Spo0F is in fact low; however, it binds Spo0F when it is in complex with Spo0B. It is proposed that the existence of a deep pocket which extends from the surface to the metal site could attract and direct the metal, thereby facilitating the metal binding of the complex.